In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or user equipments (UE), communicate via a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas, which may also be referred to as a beam or a beam group, with each service area or cell area being served by a radio network node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a “NodeB” or “eNodeB”. A service area or cell area is a geographical area where radio coverage is provided by the radio network node. The radio network node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio network node.
A Universal Mobile Telecommunications System (UMTS) is a third generation (3G) telecommunication network, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). The UMTS terrestrial radio access network (UTRAN) is essentially a RAN using wideband code division multiple access (WCDMA) and/or High Speed Packet Access (HSPA) for user equipments. In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, and investigate enhanced data rate and radio capacity. In some RANs, e.g. as in UMTS, several radio network nodes may be connected, e.g., by landlines or microwave, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC), which supervises and coordinates various activities of the plural radio network nodes connected thereto. This type of connection is sometimes referred to as a backhaul connection. The RNCs and BSCs are typically connected to one or more core networks.
Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network. The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio network nodes are directly connected to the EPC core network rather than to RNCs. In general, in E-UTRAN/LTE the functions of an RNC are distributed between the radio network nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio network nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio network nodes, this interface being denoted the X2 interface. EPS is the Evolved 3GPP Packet Switched Domain.
Paging and Tracking
Paging is a procedure that may be used for network initiated connection setup e.g. when a UE is in an RRC_IDLE state in case of LTE. In LTE, the UE camps on a selected cell and monitors the Layer 1 (L1)/Layer 2 (L2) control signaling for paging messages.
While the UE is in RRC_IDLE state its location is known by the LTE network at Tracking Area (TA) level, i.e. on a TA granularity, instead of cell level. An operator defines a group of neighbor eNBs as a TA. A TA may be made up of cells or eNBs.
A paging cycle is defined, allowing the UE to sleep most of the time and only briefly wake up to monitor L1/L2 control signaling. The maximum and most power efficient paging cycle in LTE is 2.56 seconds. Future networks will support even longer paging cycles e.g. 24 hours for Massive Machine Type Communication (M-MTC) devices and applications.
The tracking area configuration in the UE is controlled by an Mobility Management Entity (MME). Since the UE location is typically not known, the paging message is transmitted across several cells in one or more tracking areas. The UE periodically wakes up and determines which tracking area that it is currently located in and in case the tracking area is not in the allowed tracking area list the UE initiates a location area update procedure in order to inform the network of its current location.
A UE may be configured with a list of tracking areas that it can move between in idle mode. This reduces the number of location area updates the UE has to perform.
Paging is normally done first in a smaller area, one of a few cells, and if the UE is not found there the network pages the UE in a larger area, e.g. all cells in the tracking area list.
Tracking and Paging Area Size
Future networks may comprise 50-500 billion devices such as UEs and other devices with very different behavior making UE optimized tracking increasingly important. However tracking requirements differ for different UEs and may also differ over time.
Small tracking areas are beneficial for UEs with:                Stationary or low mobility;                    Predictable low mobility for extended time duration such as e.g. smart phone at night or in drawer;            Long DRX and/or low user-plane activity, allowing for a small number of paging attempts.                        Large tracking areas (or large TA lists) beneficial for UEs with                    High mobility (to enable fewer location area updates);            Short DRX (high user-plane activity) i.e. UEs that can read paging channels often.                        
From the network point of view the design of tracking areas also involves several conflicting objectives:                TAC and sync-signal may need to be transmitted often when UEs wake up from long DRX with high clock uncertainty which is costly;        Small tracking areas create many LA-updates or requires large TA-lists which results in increased signaling costs;        Large tracking areas increase the paging load in the network which results in increased signaling costs;        Transmission of Tracking Area Code (TAC) requires network nodes to periodically become active, which increases network node energy consumption.        
NX System Information Acquisition
5G-NX, sometimes denoted 5G new radio (NR), is a new Radio Access Technology (RAT) designed to meet 5G system requirements. There are three main challenges that need to be addressed by 5G wireless communication systems to enable a truly Networked Society, where information can be accessed and data shared anywhere and anytime, by anyone and anything. These are:                A massive growth in the number of connected devices.        A massive growth in traffic volume.        An increasingly wide range of applications with varying requirements and characteristics.        
To handle massive growth in traffic volume, wider frequency bands, new spectrum, and in some scenarios denser deployment are needed.
For 5G-NX, also referred to as 5G-NR, an index-based system information distribution concept is considered. The 5G-NX discusses a two-step mechanism for transmitting access information, comprising an Access Information Table (AIT). The AIT comprises a list of access information configurations and a short System Signature Index (SSI) which provides an index pointing to a certain configuration in the AIT, defining the access information, see FIG. 1.
FIG. 1 depicts the principle of AIT and SSI transmissions from a network node to a UE in a 5G-NX system. The top part of FIG. 1 depicts a time-frequency grid with periodic transmissions of SSI and AIT information. The bottom part of FIG. 1 depicts how the SSI is used to derive access information from the AIT.
The content of the AIT is assumed to be known by the UE when performing a random access attempt. The AIT in the UE may e.g. be updated in two ways;
1. A Common AIT (C-AIT) is broadcasted by the network, typically with a longer periodicity than the SSI e.g. every 500 ms or so. In some deployments the C-AIT periodicity may be the same as the SSI periodicity (e.g. in small indoor networks) and the maximum C-AIT periodicity may be very large e.g. 10 seconds in order to support extremely power limited scenarios (e.g. off-grid solar powered base stations).
2. A Dedicated AIT (D-AIT) transmitted to the UE using dedicated signaling in a dedicated beam after initial system access. The UE specific D-AIT may use the same SSIs to point to different configurations for different UEs. For instance, in the case of system congestion, this would allow to have different access persistency values for different UEs.
The SSI period is typically shorter than that of the C-AIT. The value is a tradeoff between system energy performance, UE energy performance and access latency in cases SSI needs to be read before access.
One delivery option for C-AIT is self-contained transmission in which all nodes transmit both C-AIT and SSI, with C-AIT entries referring only to themselves. However, there may be heavy interference for C-AIT reception within a synchronized network on the same frequency. To avoid C-AIT interference, C-AIT may be time-shifted in different networks.
FIG. 2 depicts more details of how the SSI and AIT principles may be implemented in 5G NR. The System Information (SI) in 5G NR is separated into “minimum SI” and “other SI”. The minimum SI is further divided into an SS Block and a transmission of system information block 1 referred to as NR-SIB1. The SS Block comprises synchronization signals primary synchronization signal referred to as NR-PSS and secondary synchronization signal referred to as NR-SSS. The combined sequence index of the NR-PSS/NR-SSS constitutes a Physical Cell Identity (PCI). In addition the SS Block comprises a Tertiary Synchronization Signal (NR-TSS) which may indicate a SS Block index in a burst of SS Blocks, denoted TSS-index in FIG. 2. In addition to the PCI index and the TSS index the Master Information Block (NR-MIB) provided inside of the Physical Broadcast Channel (NR-PBCH) may comprise an additional System Information Configuration Index (SICI), not shown in FIG. 2. In addition to the SS Block the minimum SI also comprises a transmission of NR-SIB1 which is provided by the Physical Downlink Control Channel (NR-PDCCH) and the Physical Downlink Shared Channel (NR-PDSCH) configured in the NR-MIB.
In the context of SSI/AIT described above in FIG. 1, any one of PCI, TSS-index or SICI, or a combination of these indexes, may be viewed as an SSI. The C-AIT described above would correspond to the NR-SIB1 in FIG. 2.
Since the configuration of the physical channels that provide NR-SIB1 are configured in the NR-MIB, the NR-SIB1 may be transmitted with explicitly configured parameters such as Demodulation Reference Signals (DMRS), scrambling, quasi-co-location assumptions, numerology, control-channel search-space, carrier, etc. This design enables a very large deployment flexibility in delivery of NR-SIB1. NR-SIB1 may e.g. comprise information relevant for more than once cell and it may be transmitted jointly from multiple network nodes. A cell is defined by the PCI which is part of the SS Block transmission. In case a cell has multiple beams the SS Block can be transmitted in each of these beams.
But the transmission NR-SIB1 is not limited to be transmitted in the same beams or cells that are used for transmission of the SS Block. And the NR-SIB1 may comprise information related to multiple beams and cells. A UE will extract the information it must know in order to access the system by combining the indexes derived from the reception of the SS Block with the information it finds in the NR-SIB1. In some deployments NR-SIB1 may even be provided by another RAT e.g. LTE.
The UE may store the NR-SIB1 and use the information later in another cell or beam in the network. In order to ensure that the information in the stored NR-SIB1 is still valid it is expected that the NR-MIB will contain additional information such as a system information valueTag and a System Information Area (SIA) code that determines the NR-SIB1 validity. In addition it is expected that the system information valueTag is associated with a validity timer, e.g. of 3 hours as in LTE.